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The Book of Universes

Dreaming up imaginary worlds was once regarded as the prerogative of science fiction. Not any more. Cosmologists have entered the field and are proposing - in all seriousness - that our universe might not be alone. Who better to introduce us to this notion than John Barrow? The author has a well-deserved reputation for presenting difficult scientific ideas to the public. The range of his books stretches from The Book of Nothing to The Infinite Book, both relevant to cosmology of a kind where one deals with universes that seem to appear out of nothing and go on to become infinitely large.

Barrow tells the story of expanding horizons. We discover that the earth is an ordinary planet going around an ordinary star in an ordinary galaxy. Clusters of these galaxies are retreating from each other, their motion indicating that the universe began with a Big Bang. But there was a rival idea, the Steady State theory. This held that, as the galaxy clusters populating a certain region of space move out of that region, their place is taken by the new subatomic particles being continually created. The process has no beginning and no end. Aesthetically it was pleasing, but investigations produced incontrovertible evidence in favour of the Big Bang. The Steady State idea had to be discarded.

It was Einstein's relativity theory that provided the equations for describing this Big Bang universe. According to the equations, there could be a wide range of different universes, all run along different lines and with their own laws of nature. However, there is another possibility. Many cosmologists are now exploring something called M-theory, which has a big bang producing a universe. Tiny regions of space within this universe then undergo their own big bangs, giving rise to further universes. These secondary universes spawn universes of their own. Even the parent universe could have been a product of such a process - one without a beginning or an end.

M-theory is a form of Steady State theory.

As the earlier Steady State theory was killed off, where are we to seek evidence that might either confirm or deny this new idea? As we probe the deeper recesses of our cosmos, we might strike lucky and find that our universe is being influenced by another one nearby. Otherwise, it is difficult to see how we can ever decide whether M-theory is the most important scientific theory of all, as is often claimed, or just an example of what this review started with: science fiction. As it turns out, exercising the brain cells in thinking about such matters is great fun, and The Book of Universes is an excellent place to start such an exploration.